S 593 
J.D23 
Copy 1 




STUDIES ON THE 

PHENOLDISULPHONIC ACID METHOD 

FOR DETERMINING NITRATES IN SOILS 



BY 

CHARLES WESLEY DAVIS 



A DISSERTATION SUBMITTED TO THE GRADUATE FACULTY 

OF THE IOWA STATE COLLEGE OF AGRICULTURE AND 

MECHANIC ARTS IN PARTIAL FULFILLMENT OF 

THE REQUIREMENTS FOR THE DEGREE OF 

DOCTOR OF PHILOSOPHY 

NO. 2 



I 



EscHENBACH Printing Company 
Easton, Pa. 

1917 



STUDIES ON THE 

PHENOLDISULPHONIC ACID METHOD 

FOR DETERMINING NITRATES IN SOILS 



BY 

CHARLEvS WESLEY DAVIS 



A DISSERTATION SUBMITTED TO THE GRADUATE FACULTY 

OF THE IOWA STATE COLLEGE OF AGRICULTURE AND 

MECHANIC ARTS IN PARTIAL FULFILLMENT OF 

THE REQUIREMENTS FOR THE DEGREE OF 

DOCTOR OF PHILOSOPHY 

NO. 2 



EschEnbach Printing Company 
Easton, Pa. 



Ni 



•V- 



LIBRARY OF CONGRESS 

RECEIVED 

JUL 151922 

DOCUMENTS DiViSJOi 



^ 



[Reprinted from the Journal of Industrial and Engineering Chemistry, 
Vol. 9, No. 3, page 290. March, 1917.] 



STUDIES ON THE PHENOLDISULFONIC ACID METHOD 
FOR DETERMINING NITRATES IN SOILS ^ 

By Charles W. Davis 
Received March 27, 1916 

According to Tiemanni^* the estimation of no sub- 
stance has so constantly occupied the attention of 
analytical chemists ("literally 'enchained' them") 
as the determination of nitric acid; and GilP^ *ays, 
"No determination requires more care, or occasions 
more trouble in its execution, or is more unsatisfactory 
when finished, than the one in question." 

Three general methods are used: 
I — The Zinc-Iron Method. 
II — The Tiemann-Schulze Method. 

Ill — The Colorimetric Method. 

The last two are direct methods. Other direct 
methods that have attracted attention are those of 
Schlossing-Reichardt/^ Crum-Lunge,!^ and Marx- 
Trommsdorf.^3 These methods are best suited only 
when relatively large amounts of nitrates are present, 
and in water analysis this would necessitate the evapora- 
tion of a large quantity of water. 

The phenoldisulfonic acid method is another direct 
method that has received much attention from soil 
chemists and soil bacteriologists during the past ten 
years. It originated with SprengeP" in 1863, then 
for some time fell into disuse, but in 1885 it was re- 
vived by Grandval and Lajoux.^i Afterwards articles 
appeared by Fox," Johnson, ^^ Lind,^^ Smith, "^ Bar- 
tram,-^ and Hazen and Clark." 

Hazen and Clark" as well as the German chemists 
have criticized the method severely. On recommenda- 
tion of the Association of the German Experiment 
Stations, 28 the Halle Station, after an investigation 
ae to the most reliable method for the determination 
of nitrates in soils and fertilizers, selected the Zinc- 
Iron Reduction Method as being the most accurate. 

» Part of The'sis submitted in partial fulfillment of the requirement 
for the Degree of Doctor of Philosophy in Agronomy in the graduate school 
of the Iowa State College, 1916. 

* Numbers refer to Bibliography at end of article. 

(0 



SOURCES OF ERRORS MENTIONED BY VARIOUS 
INVESTIGATORS 

Leeds, ^^ Fox,^^ ^nd GilP^ have found losses of 
nitrates ' on the water bath. Chamot and Pratt* 
report losses small on a water bath except when chlor- 
ides are present. 

Many writers have found interference in determina- 
tions in the presence of organic matter due in part to 
the masking of the yellow tint, besides certain fioc- 
culents as carbon black, potash alum,'^ aluminum 
cream, copper sulfate, etc., used to precipitate clay 
and organic matter occasions considerable loss in 
nitrates. 

GilP^ and Weston^^ found losses in the presence of 
carbonates, while Chamot and Pratt* claim losses of 
nitrates insignificant except when the quantities of 
nitrates are low or the alkalinity of the solution very 
high. 

Lipman and Sharp, ^ and Kelly^ call attention to 
great losses in the determination due to presence of 
sulfates either in the solutions, or when sulfates as 
potash alum are used as a flocculent. 

Chlorides seem to be the greatest interfering salt as 
evidenced by the investigations of Gill,^^ Stewart and 
Greaves,*" and Chamot and Pratt.* 

The latter investigators also point out the inter- 
ference of chloroform when used in soil solution to 
prevent denitrification. They also show that the 
presence of iron produces a brown or red solution, 
thus affecting the desired yellow color of the nitro- 
phenoldisulfonate. 

REAGENTS AND APPARATUS 

I — All reagents were tested for purity before using. 

2 — The standard nitrate solutions were made up 
according to the U. S. Bureau of Soils,* and used in 
the determination of nitrates in the first eight tables of 
results shown herein. The standard solution for the 
remainder of determinations was made after Hill's 
procedure.® 

3 — Throughout the whole work Chamot and Pratt's' 
modified phenoldisulfonic acid reagent was used. 

4 — The color was always developed with a concen- 
trated potassium hydroxide solution. 

5 — Colors were compared in the regulation com- 
paring tubes. The Sargent-Kennicolt colorimeter was 
used occasionally as a check on the work. 

(2) 



In obtaining results as shown in Tables XV and XVI, 
the writer used a colorimeter manufactured by Lenz 
and Naumann, New York. 

Known amounts of nitrates were measured from 
standard potassium nitrate solution by means of 
pipettes. 

EFFECT OF AMMONIA FUMES ON THE DETERMINATION 

It was thought advisable to ascertain if ammonia 
fumes in the laboratory would affect the results in the 
evaporating process on the water bath. Shallow 
dishes containing ammonium hydroxide were placed in 
the hood. Here samples of known nitrate content 
were evaporated and compared with samples evaporated 
in the laboratory. The ammonia fumes did not 
affect the results. In a second experiment ammonium 
hydroxide was boiled in the hood with other samples, 
so that the fumes were given off profusely, and these 
samples were evaporated; nitrates were determined and 
compared with samples evaporated away from the 
presence of ammonia. In this second experiment no 
loss of nitrates was obtained. 

EFFECT OF DELAY IN APPLICATION OF PHENOLDISULFONIC 
ACID AFTER EVAPORATION 

A series of nitrate solutions was evaporated to 
dryness, and after a delay of 24, 48 and 72 hours, the 
phenoldisulfonic acid was added. The results showed 
that the delay in the application of the phenoldi- 
sulfonic acid had no effect whatever. 

A second series was prepared and equal quantities 
of the acid were applied immediately after evaporation 
and left in contact unequal periods of time. Table I 
shows the results of this experiment: 

Table I 

Time in Contact. 10 min. 30 min. 1 hr. 24 hrs. 

Nitrates Added (G.) 0.004 0.004 0.004 0.004 

Nitrates Found (G.) 0.004 0.004 0.0035 0.0035 

EFFECT OF LIGHT AND TIME ON COLOR MATERIAL 

Three solutions were prepared and the color devel- 
oped. No. I was read immediately. No. -2 was left 
on the laboratory desk for 24 hours. It was thus ex- 
posed to light for about 12 hours. No. 3 was placed 
in the dark room for 24 hours. From the results 
(Table II), we conclude that readings should be made 
without delay after the color is developed. 

(3) 



Tablb II 

Mg, Nitrates 
No. Treatment Added Found 

1 Immediate reading 0.0040 0.0040 

2 Left on laboratory desk 24 hours 0.0040 0.0025 

3 Left in dark room 24 hours . 0040 . 0036 

METHODS OF APPLYING THE ACID 

The next experiment was planned for the purpose 
of finding the effect of method of applying the phenol- 
disulfonic acid to the dry residue in the nitrate de- 
termination. The acid was applied to the salt as fol- 
lows: (i) without stirring; (2) while stirring with a 
glass rod; (3) while hot. No variation was found 
in the results. 

EFFECT OF TEMPERATURE WHILE POTASSIUM HYDROXIDE 
IS BEING ADDED 

At various times we observed that in the application 
of potassium hydroxide for the purpose of developing 
the color much heat was evolved and sometimes 
violent action occurred. A series of experiments was 
carried on to find the influence of temperature during 
the time the alkali was being added, with the results 
given in Table III. 

Table III 

Mg. Mg. 

Nitrates Nitrates 

No. Treatment op Solution Added Found 

1 Kept at room temperature 0.010 0.010 

2 Heated by reaction 0.010 0.010 

3 Heated to 80° C. 0.010 0.010 

4 Heated to 100° C. 0.010 0.010 

5 At freezing temperature (on ice) 0.010 0.0096 

EFFECT OF CONCENTRATED SOLUTION WHEN POTASSIUM 
HYDROXIDE IS ADDfeD 

After the application of phenoldisulfonic acid, 
when the salt is taken up with water, if the solution is 
highly concentrated, a precipitate is sometimes formed 
on the addition of KOH. This phenomenon suggested 
a series to find whether the concentration of the solu- 
tion at this point affected the results. Table IV shows 
no variation in results whether the solution just before 
the addition of potassium hydroxide was dilute or 
concentrated. 

Table IV 

Mg. Mg. 

Nitrates Nitrates 

No. Solution Cc. Added Found 

1 Concentrated 25 0.025 0.025 

2 Concentrated 25 "^ 0.025 0.025 

3 Dilute 50 0.025 0.025 

4 Dilute 50 0.025 0.025 

EFFECT OF VARIOUS SALTS 

The writer carried on experiments to ascertain the 
effects of NaCl, Na2S04, NasCOs, and mixed alkali 
salts on the loss of nitrates. These results confirm 

(4) 



in a general way the results of Lipman and Sharp* 
in experiments with these same salts. 

EFFECT OF NaC2H302 

Since Lipman^ as well as the writer found the effect 
of chlorides, sulfates, and carbonates to decrease in 
the order mentioned, the latter producing slight loss, 
if any, it was believed a weak acid with a strong base 
might not occasion any loss whatever. From i to 
20 mg. of sodium acetate were used in a solution 
containing 0.025 mg., no loss of nitrates being noticed. 

EFFECT OF VARYING AMOUNTS OF STANDARD NITRATE 

SOLUTION AND UNIFORM AMOUNTS OF PHENOL- 

DISULFONIC ACID 

A series with a nitrate content from 0.0125 to 0.200 
mg. was now analyzed using uniform amounts of 
phenoldisulfonic acid (2 cc.) throughout and compared 
with standard of 0.025 mg. having been treated with 
2 cc. of phenoldisulfonic acid. The loss here with the 
sample lowest in nitrates was 4 per cent; the sample 
highest in nitrates lost 30 per cent. (See Table V.) 

Table V — 2 cc. Phenoldisulfonic Acid Added in Each Case 

Mg- Nitrates Added 0.0125 0.0250 0.0500 0.0750 0.1000 0.2000 

m|: Nitratel Found...... 0.0120 0.0250 0.0446 0.0625 0.0832 0.1388 

EFFECTS OF VARYING AMOUNTS OF NITRATE WITH 
VARYING AMOUNTS OF PHENOLDISULFONIC ACID 

It was then decided to increase the amount of phenol- 
disulfonic acid in proportion to the amount of nitrates 
used: 2 cc. of this acid were used for every 0.025 
mg. of nitrate. In this way a greater per cent 
of nitrates was recovered from the artificial solution. 
Here the maximum loss was only 10 per cent as com- 
pared with a loss of 30 per cent in Table V. 

Table VI 

Cc. Disulfonic Acid 12 4 6 8 16 

TUcr Nitrates Added 0.0125 0.0250 0.0500 0.0750 0.1000 0.2000 

MliNStrttes Found::::.: 0.0125 0.0250 0.0500 0.0695 0.0892 0.1800 

MEANS OF PREVENTING LOSS OF NITRATES BY THE 
PHENOLDISULFONIC ACID METHOD 

The results of the last two experiments demonstrated 
the fact that when the nitrate solution approaches loo 
parts per million, or more, the loss of nitrates is great 
even when there are no interfering salts present, such 
as chlorides, sulfates, etc. On further investigation 
the writer was convinced that much loss took place 
on the water bath as had been suggested by Lipman^ 
and others. 

(5) 



Three things suggested dissociation of KNO3 on the 
water bath: (i) Slight or no loss of nitrates when 
sodium carbonate was added before evaporation; 
(2) recovery of more nitrates in soil solution when CaO 
is used as a substitute for alum in precipitating the 
clay in a soil solution. Not only does the use of CaO 
prevent the loss occasioned by the SO4 radical, as in the 
case when alum is used as a fiocculent, but the fact 
that CaO is an alkali prevents the loss of nitrates when 
the KNO3 dissociates by uniting and forming Ca(N03)2. 
An excess of alkali prevents the formation of nitric 
acid; (3) a bit of blue litmus paper was placed in the 
KNO3 solution and it was noticed to have turned red 
just before the solution became dry. This was the 
first clue that furnished a solution for the prevention 
of loss of nitrates on the water bath. 

EFFECT OF ADDING AMMONIA TO THE POTASSIUM NITRATE 
SOLUTION BEFORE EVAPORATION 

Since it had already been found that ammonia 

fumes did not affect the loss or gain of nitrates, a series 

was run in which each sample was kept ammoniacal 

during evaporation. The results were as anticipated 

as will be seen in Table VII. 

Table VII 

Mg. Nitrates Added 0.0125 0.0250 0.0500 0.0750 O.IOOO 

Mg. Nitrates Found 0.0125 0.0250 0.0500 0.0760 O.IOIO 

In the last experiment the five samples were com- 
pared to a standard containing 0.025 mg. of KNO3, 
to which no ammonia had been added before evapora- 
tion as in case with the samples above. 

EFFECT OF POTASH ALUM [K2Al2(S04)4 ] 

It was desired, if possible, to prevent loss occasioned 
by the use of potash alum as a fiocculent in preparing 
the soil solutions for analysis. 

Lipman and Sharp, ^ in speaking of the phenoldi- 
sulfonic acid method in determining nitrates, say: 
"So that while we deem it unsafe in the presence of 
considerable quantities of salts containing chlorides and 
sulfates to determine nitrates by the phenoldisulfonic 
acid method, and would therefore recommend the 
Street modification of the Ulsch method^* in such 
cases, it is likewise clear that many of the nitrate de- 
terminations made in soil laboratories, as is especially 
the case in soil bacteriological work, would not be 
interfered with by salts. In such cases the method can 
be safely depended upon if potash alum, aluminum 
cream and bone-black are not used to coagulate the 

(6) 



clay and organic matter, since they have been found in 
the researches above described to be productive of very 
serious errors." 

Since ammonia is highly volatile, potassium hy- 
droxide was substituted in keeping the solution al- 
kaline on the water bath. This prevented the loss of 
nitrates on the water bath, so that we were able to 
recover all nitrates when the samples contained from 
5 to 150 mg. of potash alum before evaporation. 
■Lipman and Sharp, ^ however, lost as high as 38 per 
cent of nitrates when they used the same amounts of 
potash alum without the addition of alkali. Table VIII 
shows a comparison of the writer's and Lipman and 
Sharp's results. 









T 


ABLE 


VIII 








Mg. 














K2Ah(S04)4 


Added 


Mo. Nitrates Added 


Mg. Nitrates Founi 


Davis 




Lipman 
5.0 


Davis 




Lipman 
0.050 


Davis 


Lipman 
0.040 


i2!5 




12.5 


o'.ois 




0.050 


0^025 


0.036 


25.0 




25.0 


0.025 




0.050 


0.025 


0.0.33 


50.0 




50.0 


0.025 




0.050 


0.025 


. 03 1 


100.0 




100,0 


0.025 




0.050 


0.025 


0.034 


150.0 




150.0 


0.025 




0.050 


0.025 


0.040 



In the previous experiment we have shown conclu- 
sively that potash alum may be used as a flocculent 
in preparing the soil solution without incurring any 
loss of nitrates; then, since potash alum is undoubtedly 
the best flocculent in precipitating clay and organic 
matter, soil chemists and soil bacteriologists may safely 
continue its use as a flocculent,, provided the solution 
is kept alkaline oti the water bath. 

EFFECT OF POTASSIUM CHLORIDE BY NEW METHOD 

We now attempted to recover all nitrates in the 
presence of the chlorine radical. A series was pre- 
pared using from i to 20 mg. KCl and evaporated 
down with excess of potassium hydroxide as in the 
previous experiment. Here equal amounts of phenol 
disulfonic acid were applied, but rather violent action 
took place. Hydrochloric acid fumes were notice- 
able. The results as shown in Table IX were start- 
ling. 

Table IX 
Mg. KCl Added 1 

Mg. Nitrates Added 0.025 

Mg. Nitrates Found 0.0125 

This loss of nitrates, of course, did not take place 
on the water bath, but at the time the phenoldisulfonic 
acid was added. There was a noticeably large residue 
of potassium salts since potassium hydroxide had been 
added to keep the solution alkaline and potassium 
chloride had been added to the series. This was 

(7) 



5 


10 


20 


0.025 
. 1 00 


0.025 
0.0050 


0.025 
0.0035 



responsible for the violent action, thus liberating 
much hydrochloric acid which in turn brought about 
losses of nitrates at this point. 

EFFECT OF Ca(0H)2 IN PREVENTING THE LOSS OF 

NITRATES IN THE PRESENCE OF CHLORIDES AT THE 

POINT WHEN THE PHENOLDISULFONIC ACID 

IS APPLIED 

To avoid the violent action when phenoldisulfonic 
acid is applied it was decided to substitute saturated 
calcium hydroxide solution for potassium hydroxide 
before evaporation. Potassium chloride was added 
in amounts as before. When the solutions went to 
dryness the residues were found to be small, and we 
hoped the difificulty had been overcome, but we were 
much disappointed as the results in Table X will 
show. 

Table X 

Mg. KCl Added 1 5 10 20 

Mg. Nitrates Added 0.025 0.025 0.025 0.025 

Mg. Nitrates Found 0.0250 0.0220 0.0195 0.0140 

Here with 20 mg. of KCl we obtained a loss of 44 
per cent. This was better than in the previous ex- 
periment, yet the loss was still too great. In the last 
experiment the chemical action was slight, but HCl 
fumes were still noticeable when the acid was applied. 

Another trial was carried out as previously, except 
that the phenoldisulfonic acid was added, slowly, 
drop by drop, in an effort to reduce the action. The 
results were as follows: 

Table XI 
Mg. KCl Added 1 

Mg. Nitrates Added 0.025 

Mg. Nitrates Found 0.023 

Still another trial was made. Nos. i, 2, 3, and the 
standard were treated as before, i. e., 4 cc. of phenoldi- 
sulfonic acid were applied to each, but in No. 4 an ex- 
cess of phenoldisulfonic acid was used (about 12 cc), 
and instead of adding the acid slowly it was flooded 
over the dry residue quickly. The results were as 
follows: 

Table XII 
No. 12 3 4 

Mg. KCl Added 1 5 10 20 

Mg. Nitrates Added 0.025 0.02'5 0.025 0.025 

Mg. Nitrates Found 0.0225 0.0220 0.0200 0.0250 

The treatment of No. 4 in Table XII shows means 
of preventing loss of nitrates at the time of applica- 
tion of phenoldisulfonic acid. We now decided to 
apply treatment of No. 4 in the above table to a whole 

(8) 



5 


10 


20 


0.025 
0.023 


0.025 
0.019 


0.025 
0.014 



series. This was done and gave results free from loss 
of nitrates. 

EFFECT OF SODIUM SULFATE BY NEW METHOD 

Kelly^ made a study of the effects of sulfates on the 
determination of nitrates, using Na2S04, (NH4)2S04, 
and CaS04. Since his greatest loss occurred in the 
presence of Na2S04 we carried out an experiment with 
this same salt by our new method. A comparison 
of our results with those of Kelly's is given in Table 
XIII below. 

Table XIII 

Mg NaiSO* Added Mg. Nitrates Added Mg. Nitrates Found 

Davis Kelly Davis Kelly Davis Kelly 

1 1 0.025 0.275 0.025 0.275 

5 5 0.025 0.275 0.025 0.265 

,0 10 0.025 0.275 0.025 0.225 

20 20 0.025 0.275 0.02o 0.180 

40 ... 0.275 ... 0.140 

The writer recovered all nitrates, while Kelly lost 
from o to 32 per cent when 20 mg., and 48 per cent 
when 40 mg. of sodium sulfate were used. 

BAER'S method COPPER SULFATE AS FLOCCULENT 

Baer" used copper sulfate as a flocculent in preparing 
soil solutions for nitrate determinations. After the 
solution was clarified with copper sulfate, aliquot 
parts were measured out into Erlenmeyer flasks and 
the copper removed by adding one gram of manganese 
oxide. The flasks were stoppered and gently warmed, 
and then filtered and washed, the filtrate was evapo- 
rated to dryness and the nitrates determined by the 
ordinary method. While CUSO4 is an excellent 
flocculent the writer has never been able to recover 
all nitrates even by the modified method. Since 
potash alum can be used as a flocculent and all nitrates 
recovered regardless of what other salts may be pres- 
ent, it seems that there is no use of attempting to 
use copper sulfate since it is necessary to remove the 
copper before the determination can be made. 

APPLYING NEW METHOD TO THE DETERMINATION OF 
NITRATES IN SOILS 

As lime, copper sulfate and alum are considered 
good flocculents, a comparison of these was made 
by the new method. Three 50-gram samples were 
prepared and placed in Mason jars with 240 cc. of 
distilled water. Ten cc. of normal solutions of CaO, 
, CUSO4 and K2Al2(S04)4 were added, respectively. 
The samples were placed in a shaker for 30 minutes and 
the determinations made by the modified method. 

(9) 



Table XIV 
Flocculent Mg Nitrates Found 

No. Used in Soil Solution 

1 CaO 0.1514 

2 CuSOi 0.925 

3 K2Al2(S04)4 0.1514 

Another sample of soil was taken and lime and alum 
were used as flocculents. The acid solution with the alum 
was tried both by new and old method. 

Table XV 

Mg. Nitrates 
No. Flocculent Used Found in Soil Solution 

1 CaO 0.1543 

2 Kj Al2(S0<)« (New Method) 0.1543 

3 K2Al2(S04)« (Old Method) . 1025 

It was now suggested that a comparison of the old 
colorimetric and modified colorimetric method be tried 
on several soils of varied nitrate content. Alum was 
used as a flocculent in each case. Samples of soil 
were taken from the following plots: Corn, fallow, 
oat stubble and alfalfa. The results are found in 
Table XVI. 

Table XVI 

Mg. Nitrates in 100 Grams of Soil 

Old New 

No. Kind of Soil Color. Method Color. Method 

1 Corn 1.1639 1.3403 

2 Fallow 0.8798 1.1639 

3 Oats 1.1060 1.1245 

4 Alfalfa 2.0382 2.0382 

You will observe that by the modified method 
greater amounts of nitrates were found with each soil 
except in case of that from the alfalfa plot; here the 
results were the same. Perhaps a heavy application 
of lime to the soil before seeding the alfalfa rendered 
this soil strongly alkaline and the presence of the 
alkali in the soil prevented loss of nitrates on the 
water bath. 

Since in the last experiment the highest amount of 
nitrates found in the soil was over 2 mg., we tested 
the reproducibility of the method in artificial solutions 
of known nitrate content, using samples from 0.55 
mg. to over 2 mg. All nitrates were recovered. 

Many investigators have asserted that the colori- 
metric method is unreliable when large amounts of 
nitrates are to be determined. This objection 
prompted an experiment to find if as much as 4 mg. 
of nitrate could be recovered in artificial solu- 
tions. All nitrates were recovered, thus showing the 
reproducibility of results. 

APPLICATION OF THE MODIFIED PHENOLDISULFONIC 
ACID METHOD TO SOIL BACTERIOLOGICAL WORK 

Frequently large amounts of nitrates are obtained 
in the nitrification experiments in soil bacteriology. 

(10) 



We decided to test the applicability of the method to 
work of this kind. 

NITRIFICATION EXPERIMENT 

Soil samples were taken from the soil plots of the 
Iowa Experiment Station. The plots were as fol- 
lows: 

Soil No. loi from timothy sod. The timothy had just 
been cut. 

Soil No. I02, peat plot. Two and eight-tenths tons 
of peat had just been added and kept fallow. 

Soil No. 107, check plot which had also been kept 
fallow. 

Two hundred-gram samples of each soil were placed 
in tumblers in duplicate: 200 mg. of (NH4)2S04 were 
dissolved in 60 cc. water and added to each tumbler. 
The incubation was carried on for three weeks at room 
temperature. The tumblers were weighed every six 
days, and the water lost by evaporation was restored. 
At the end of three weeks the nitrates were determined 
as follows: The samples were placed in shaker bottles 
with 800 cc. of water. Alum was used as the floccu- 
lent. After the samples had been shaken 30 minutes, 
25-cc. portions, in duplicate, were evaporated to dry- 
ness with 15 cc. of saturated Ca(0H)2 solution. The 
samples were treated with 5 cc. portions of phenoldi- 
sulfonic acid and compared with standard. Table 
XVII shows the large amounts of nitrate found. 

That large amounts of nitrates can be determined 
by the phenoldisulfonic acid method is here demon- 
strated. In Table XVII from 6 to 15 times as much 

Table XVII 

Mg. N Found as Nitrate per 100 g. 
Soil No. Plot Soil Duplicates 

101 Timothy 62.774 58.250 

102 Peat 66.086 57.564 

107 Check 35.786 29 016 

nitrate was determined as in the preceding experi- 
ments where known amounts of nitrates were used. 
Should soils contain larger amounts of nitrates than 
those used in Table XVII one need only to reduce the 
amount of aliquot part of soil solution taken for the 
determination. 

SUMMARY 
I STUDIES ON THE OLD METHOD 

I — Ammonia fumes in the laboratory do not affect 
the result in the determination of nitrates by the 
phenoldisulfonic acid method. 

(II) 



2 — Light affects the color material and readings 
should be made without delay. 

3 — Applying phenoldisulfonic acid without stirring, 
stirring with a rod, or applying while hot shows no 
difference in results. 

4 — The temperature of the solution at the time alkali 
is added to develop color shows no variation in results 
except at freezing temperature when a loss of 4 parts 
per million is found in a loo-part-per-million solu- 
tion. 

5 — In checking up Lipman and Sharp's work, 
"Studies on the Phenoldisulfonic Acid Method for 
Determining Nitrates in Soils," we found the loss of 
nitrates occasioned by the addition of various salts to 
correspond with the results of these investigators, 
the maximum loss being caused by the chlorine radical, 
and decreasing with sulfates and carbonates — the 
latter producing no loss. The addition of a weak acid 
(sodium acetate) produced no loss of nitrates what- 
ever. 

6 — Potassium chloride added just before and just 
after the developing of the color by potassium hydroxide 
produced no loss of nitrates. 

7 — When uniform amounts of phenoldisulfonic acid 
(2 cc.) were used the maximum loss of nitrates was 
30 per cent; when proportional amounts of phenoldi- 
sulfonic acid were used {i. e., 2 cc. for each 0.025 n^g-). 
the maximum loss was reduced to 10 per cent. 

II PREVENTING LOSS OF NITRATES BY A MODIFIED 

METHOD 

I — Loss of nitrates was found to take place on the 
water bath, and this loss was prevented by keeping 
the solution alkaline during the process of evapora- 
tion. 

2 — The addition of two drops of HCl in a solution 
containing 25 parts per million of nitrates caused a loss 
of all nitrates. 

3 — By the modified method we were able to prevent 
the loss of nitrates in the presence of chlorides, sul- 
fates and carbonates. 

4 — When chlorides were present, a loss of nitrates 
was found to take place on the addition of the phenol- 
disulfonic acid. This loss was overcome by evapora- 
ting the solution to dryness with excess of Ca(0H)2, 
and flooding an excess of phenoldisulfonic acid quickly 
over the salt. 

(12) 



5 — All nitrates in a soil solution can be recovered 
regardless of the salts present therein. 

6 — Potash alum may be used as a flocculent in pre- 
paring the soil solution without producing a loss of 
nitrates. By the old method the loss of nitrates in the 
presence of certain salts was often as high as 50 per 
cent. 

7 — Since potash alum is an excellent flocculent, soil 
chemists and soil bacteriologists need not hesitate to 
employ its use, provided they use the modified phenol- 
disulfonic acid method. 

BIBLIOGRAPHY 

' Schreiner anri Failyer, "Colorimetric, Turbidity and Titration Meth- 
ods Used in Soil Investigations," Bureau of Soils, U. S. Dept. Agri., Bull 
31. 

' C. B. Lipman and L. T. Sharp. "Studies on the Phenoldisulphonic 
Acid Method for Determining Nitrates in Soils," Univ. Cal.Pub.in Air. 
Sci., Vol. 1, No. 2. 

» E. M. Chamot and D. S. Pratt, "A Study of the Phenoldisulfonic Acid 
Method for the Determination of Nitrates in Water — The Composition 
of the Yellow Compound," Jour. Am. Chem. Soc. Vol. 32, pp. 630-637. 

« E. M. Chamot. D. S. Pratt and H. W. Redfield, "A Study on the 
Phenoldisulfonic Acid Method for the Determination of Nitrates in Water — 
the Chief Sources of Error in the Method," Jour. Am. Chem. Soc, Vol. 33, 
pp. 366-381. 

' E. M. Chamot, D. S. Pratt and H. W. Redfield, "A Study of the 
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Water — A Modified Phenoldisulfonic Acid Method," Ibid., Vol. 33, pp. 
381-384. 

' H. H. Hill, "The Determination of Nitrates in Soil and Soil Extracts," 
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' W. P. Kelly, "The Effects of Sulfates on the Determination of Ni- 
trates," Jour. Am. Chem. Soc, 36 (1913), 775. 

* Robert Stewart, "The Occurrence of Potassium Nitrate in Western 
America," Jour. Am. Chem. Soc, 33 (1911), 1952. 

• R. Stewart and J. E. Greaves. "The Influence of Chlorine on the 
Determination of Nitrates by the Phenoldisulfonic Acid Method," Jour. 
Am. Chem. Soc, 35 (1913), 579. 

'" R. Stewart and J. E. Greaves, "The Influence of Chlorine upon the 
Determination of Nitric Nitrogen," Ibid., 32 (1910), 756. 

11 E. M. Chamot and D. S. Pratt, "A Study of the Phenoldisulfonic 
Acid Method for the Determination of Nitrates in Water — The Composi- 
tion of the Reagent and the Reaction Product." Jour. Am. Chem. Soc, 
31 (1909), 922. 

'2 A. H. Gill, "On the Determination of Nitrates in Potable Water," 
Jour. Am. Chem. Soc, 16 (1894), 122. 

13 King and Whitson. Wis. Agri. Exp Sta., Bulls. 85 and 93. 

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!• Tiemann-Gaertner "Wasseranalyse," 3rd Ed., p. 168. 

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'• Crum-Lunge, Phil. Man.. [3] 30, 426. 

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" Fox, Tech. Quart.. 1, 1. 

(13) 



M Johnson, Chem. News, 61, 15. 

''* Lind, Chem. News, 58, 1,15, 28. 

25 Smith, Analyst, 10, 197. 

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M Hazen and Clark. 7. Anal. Appl. Chem.. 5, I. 

i» Exp. Sia. Record, 5, 404. 

s» Fox, Tec/t. Quart., 1, 54. 

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» XJlsch. New .Jersey Expt. Sta. Kept. 1892, 188-193. 

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